Versican degradation and vascular disease

A new VCAN/versican splice acceptor site mutation in a French Wagner family associated with vascular and inflammatory ocular features

PURPOSE

To detail the highly variable ocular phenotypes of a French family affected with an autosomal dominantly inherited vitreoretinopathy and to identify the disease gene.

METHODS

Sixteen family members with ten affected individuals underwent detailed ophthalmic evaluation. Genetic linkage analysis and gene screening were undertaken for genes known to be involved in degenerative and exudative vitreoretinopathies. Qualitative reverse transcriptase-PCR analysis of the versiscan (VCAN) transcripts was performed after mutation detection in the VCAN gene.

RESULTS

The first index patient of this French family was referred to us because of a chronic uveitis since infancy; this uveitis was associated with exudative retinal detachment in the context of a severe uncharacterized familial vitreoretinopathy. Genetic linkage was obtained to the VCAN locus, and we further identified a new pathogenic mutation at the highly conserved splice acceptor site in intron 7 of the VCAN gene (c.4004-2A>T), which produced aberrantly spliced VCAN transcripts.

CONCLUSIONS

Extensive molecular investigation allowed us to classify this familial vitreoretinopathy as Wagner syndrome. This study illustrates the need to confirm clinical diagnosis by molecular genetic testing and adds new ocular phenotypes to the Wagner syndrome, such as vascular and inflammatory features.

Adamts5 deletion blocks murine dermal repair through CD44-mediated aggrecan accumulation and modulation of transforming growth factor β1 (TGFβ1) signaling

ADAMTS5 has been implicated in the degradation of cartilage aggrecan in human osteoarthritis. Here, we describe a novel role for the enzyme in the regulation of TGFβ1 signaling in dermal fibroblasts both in vivo and in vitro. Adamts5(-/-) mice, generated by deletion of exon 2, exhibit impaired contraction and dermal collagen deposition in an excisional wound healing model. This was accompanied by accumulation in the dermal layer of cell aggregates and fibroblastic cells surrounded by a pericellular matrix enriched in full-length aggrecan. Adamts5(-/-) wounds exhibit low expression (relative to wild type) of collagen type I and type III but show a persistently elevated expression of tgfbRII and alk1. Aggrecan deposition and impaired dermal repair in Adamts5(-/-) mice are both dependent on CD44, and Cd44(-/-)/Adamts5(-/-) mice display robust activation of TGFβ receptor II and collagen type III expression and the dermal regeneration seen in WT mice. TGFβ1 treatment of newborn fibroblasts from wild type mice results in Smad2/3 phosphorylation, whereas cells from Adamts5(-/-) mice phosphorylate Smad1/5/8. The altered TGFβ1 response in the Adamts5(-/-) cells is dependent on the presence of aggrecan and expression of CD44, because Cd44(-/-)/Adamts5(-/-) cells respond like WT cells. We propose that ADAMTS5 deficiency in fibrous tissues results in a poor repair response due to the accumulation of aggrecan in the pericellular matrix of fibroblast progenitor cells, which prevents their transition to mature fibroblasts. Thus, the capacity of ADAMTS5 to modulate critical tissue repair signaling events suggests a unique role for this enzyme, which sets it apart from other members of the ADAMTS family of proteases.

A link between smooth muscle cell death and extracellular matrix degradation during vascular atrophy

OBJECTIVE

High blood flow induces neointimal atrophy in polytetrafluoroethylene (PTFE) aortoiliac grafts and a tight external PTFE wrap of the iliac artery induces medial atrophy. In both nonhuman primate models, atrophy with loss of smooth muscle cells and extracellular matrix (ECM) begins at ≤4 days. We hypothesized that matrix loss would be linked to cell death, but the factors and mechanisms involved are not known. The purpose of this study was to determine commonly regulated genes in these two models, which we hypothesized would be a small set of genes that might be key regulators of vascular atrophy.

METHODS

DNA microarray analysis (Sentrix Human Ref 8; Illumina, San Diego, Calif; ∼23,000 genes) was performed on arterial tissue from the wrap model (n = 9) and graft neointima from the graft model (n = 5) 1 day after wrapping or the switch to high flow, respectively. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was also performed. Expression of this vascular atrophy gene set was also studied after Fas ligand-induced cell death in cultured smooth muscle cells and organ cultured arteries.

RESULTS

Microarray analysis showed 15 genes were regulated in the same direction in both atrophy models: 9 upregulated and 6 downregulated. Seven of nine upregulated genes were confirmed by qRT-PCR in both models. Upregulated genes included the ECM-degrading enzymes ADAMTS4, tissue plasminogen activator (PLAT), and hyaluronidase 2; possible growth regulatory factors, including chromosome 8 open reading frame 4 and leucine-rich repeat family containing 8; a differentiation regulatory factor (musculoskeletal embryonic nuclear protein 1); a dead cell removal factor (ficolin 3); and a prostaglandin transporter (solute carrier organic anion transporter family member 2A1). Five downregulated genes were confirmed but only in one or the other model. Of the seven upregulated genes, ADAMTS4, PLAT, hyaluronidase 2, solute carrier organic anion transporter family member 2A1, leucine-rich repeat family containing 8, and chromosome 8 open reading frame 4 were also upregulated in vitro in cultured smooth muscle cells or cultured iliac artery by treatment with FasL, which causes cell death. However, blockade of caspase activity with Z-VAD inhibited FasL-mediated cell death, but not gene induction.

CONCLUSION

Seven gene products were upregulated in two distinctly different in vivo nonhuman primate vascular atrophy models. Induction of cell death by FasL in vitro induced six of these genes, including the ECM-degrading factors ADAMTS4, hyaluronidase 2, and PLAT, suggesting a mechanism by which the program of tissue atrophy coordinately removes extracellular matrix as cells die. These genes may be key regulators of vascular atrophy.

Proteolytic cleavage of versican and involvement of ADAMTS-1 in VEGF-A/VPF-induced pathological angiogenesis

Malignant tumors and chronic inflammatory diseases induce angiogenesis by overexpressing vascular endothelial growth factor A (VEGF-A/VPF). VEGF-A-induced pathological angiogenesis can be mimicked in immunoincompetent mice with an adenoviral vector expressing VEGF-A(164) (Ad-VEGF-A(164)). The initial step is generation of greatly enlarged "mother" vessels (MV) from preexisting normal venules by a process involving degradation of their rigid basement membranes. Immunohistochemical and Western blot analyses revealed that versican, an extracellular matrix component in the basement membranes of venules, is degraded early in the course of MV formation, resulting in the appearance of a versican N-terminal DPEAAE fragment associated with MV endothelial cells. The protease ADAMTS-1, known to cleave versican near its N terminus to generate DPEAAE, is also upregulated by VEGF-A in parallel with MV formation and localizes to the endothelium of the developing MV. The authors also show that MMP-15 (MT-2 MMP), a protease that activates ADAMTS-1, is upregulated by VEGF-A in endothelial cells in vitro and in vivo. These data suggest VEGF-A initiates MV formation, in part, by inducing the expression of endothelial cell proteases such as ADAMTS-1 and MMP-15 that act in concert to degrade venular basement membrane versican. Thus, versican is actively processed during the early course of VEGF-A-induced pathological angiogenesis.

Developing vasculature and stroma in engineered human myocardium

We recently developed a scaffold-free patch of human myocardium with human embryonic stem cell-derived cardiomyocytes and showed that stromal and endothelial cells form vascular networks in vitro and improve cardiomyocyte engraftment. Here, we hypothesize that stromal cells regulate the angiogenic phenotype by modulating the extracellular matrix (ECM). Human marrow stromal cells (hMSCs) support the greatest degree of endothelial cell organization, at 1.3- to 2.4-fold higher than other stromal cells tested. Stromal cells produce abundant ECM components in patches, including fibrillar collagen, hyaluronan, and versican. We identified two clonal hMSC lines that supported endothelial networks poorly and robustly. Interestingly, the pro-angiogenic hMSCs express high levels of versican, a chondroitin sulfate proteglycan that modulates angiogenesis and wound healing, whereas poorly angiogenic hMSCs produce little versican. When transplanted onto uninjured athymic rat hearts, patches with proangiogenic hMSCs develop ~ 50-fold more human vessels and form anastomoses with the host circulation, resulting in chimeric vessels containing erythrocytes. Thus, stromal cells play a key role in supporting vascularization of engineered human myocardium. Different stromal cell types vary widely in their proangiogenic ability, likely due in part to differences in ECM synthesis. Comparison of these cells defines an in vitro predictive platform for studying vascular development.

Differentiation of cardiomyocytes from human embryonic stem cells is accompanied by changes in the extracellular matrix production of versican and hyaluronan

Proteoglycans and hyaluronan play critical roles in heart development. In this study, human embryonic stem cells (hESC) were used as a model to quantify the synthesis of proteoglycans and hyaluronan in hESC in the early stages of differentiation, and after directed differentiation into cardiomyocytes. We demonstrated that both hESC and cardiomyocyte cultures synthesize an extracellular matrix (ECM) enriched in proteoglycans and hyaluronan. During cardiomyocyte differentiation, total proteoglycan and hyaluronan decreased and the proportion of proteoglycans bearing heparan sulfate chains was reduced. Versican, a chondroitin sulfate proteoglycan, accumulated in hESC and cardiomyocyte cultures. Furthermore, versican synthesized by hESC contained more N- and O-linked oligosaccharide than versican from cardiomyocytes. Transcripts for the versican variants, V0, V1, V2, and V3, increased in cardiomyocytes compared to hESC, with V1 most abundant. Hyaluronan in hESC had lower molecular weight than hyaluronan from cardiomyocyte cultures. These changes were accompanied by an increase in HAS-1 and HAS-2 mRNA in cardiomyocyte cultures, with HAS-2 most abundant. Interestingly, HAS-3 was absent from the cardiomyocyte cultures, but expressed by hESC. These results indicate that human cardiomyocyte differentiation is accompanied by specific changes in the expression and accumulation of ECM components and suggest a role for versican and hyaluronan in this process.

The quantification of ADAMTS4 and 8 expression and selection of reference genes for quantitative real-time PCR analysis in myocardial infarction

INTRODUCTION

ADAMTS4 and ADAMTS8 are proteases involved in ECM proteolysis and antiangiogenesis, but little is known about their expression and function in myocardial infarction (MI). We examined ADAMTS4 and ADAMTS8 expression in a rat MI model by quantitative real-time polymerase chain reaction (qPCR) and enzyme linked immunosorbent assay (ELISA). The expressions of glyseraldehyde-3-phosphate dehydrogenase (GAPDH), beta-actin (ACTB), acidic ribosomal phosphoprotein P0 (ARBP), and ribosomal protein L13A (RPL13A) were examined in order to validate the appropriate housekeeping genes after MI.

METHODS

Male Wistar rats were subjected to MI, and infarcted myocardial tissue was collected at 3, 6, 12, 24h, 3, 7, 14 and 21days after MI. ADAMTS4, ADAMTS8, and the four housekeeping genes were quantified using qPCR and the expression stability of the four housekeeping genes was investigated using GeNorm software. The protein levels of ADAMTS4 were detected using ELISA kits.

RESULTS

The M values of GAPDH, ACTB, ARBP and RPL13A were 0.721, 1.2, 0.812 and 0.812 respectively. GAPDH and ARBP were ranked the most stable genes. ADAMTS4 mRNA increased at 3h after MI, peaked at 6h, then decreased rapidly. ADAMTS8 mRNA increased at 6h, peaked at 24h, remained high at 3d, then decreased gradually. The protein levels of ADAMTS4 were significantly increased at 6h, 12h, 24h and 3d after MI.

CONCLUSION

The results suggest that GAPDH and ARBP are two appropriate housekeeping genes for the rat MI model. Both ADAMTS4 and ADAMTS8 mRNA levels and ADAMTS4 protein level increased, but they exhibited different expression profiles.

Proteoglycans: key regulators of pulmonary inflammation and the innate immune response to lung infection

Exposure to viruses and bacteria results in lung infections and places a significant burden on public health. The innate immune system is an early warning system that recognizes viruses and bacteria, which results in the rapid production of inflammatory mediators such as cytokines and chemokines and the pulmonary recruitment of leukocytes. When leukocytes emigrate from the systemic circulation through the extracellular matrix (ECM) in response to lung infection they encounter proteoglycans, which consist of a core protein and their associated glycosaminoglycans. In this review, we discuss how proteoglycans serve to modify the pulmonary inflammatory response and leukocyte migration through a number of different mechanisms including: (1) The ability of soluble proteoglycans or fragments of glycosaminoglycans to activate Toll-like receptor (TLRs) signaling pathways; (2) The binding and sequestration of cytokines, chemokines, and growth factors by proteoglycans; (3) the ability of proteoglycans and hyaluronan to facilitate leukocyte adhesion and sequestration; and (4) The interactions between proteoglycans and matrix metalloproteinases (MMP) that alter the function of these proteases. In conclusion, proteoglycans fine-tune tissue inflammation through a number of different mechanisms. Clarification of the mechanisms whereby proteoglycans modulate the pulmonary inflammatory response will most likely lead to new therapeutic approaches to inflammatory lung disease and lung infection.

Versican targeting by RNA interference suppresses aggregative growth of dermal papilla cells

BACKGROUND

Dermal papilla cells (DPCs) are specialized fibroblasts found in the hair follicle papilla, which are associated with the development and cycle regulation of hair follicles (HFs). DPCs exhibit a multilayer aggregative growth character, which is closely related to induction of HF formation. Versican, a large chondroitin sulphate proteoglycan and one of the major components of the extracellular matrix, is involved in the formation of HF.

METHODS

To confirm the relationship between versican and the aggregative growth of DPCs, we first induced and established an aggregative cell model in DPCs in vitro, with cells taken to passage 8. Simultaneously, aggregative passage 2 DPCs and nonaggregative passage 8 DPCs were selected as parallel controls. RNA interference (RNAi) targeted to versican was used in passage 2 DPCs using a lentiviral vector. Reverse transcriptase (RT)-PCR and western blotting were used to assay the expression of versican in DPCs.

RESULTS

RNAi targeted to versican efficiently suppressed the aggregative growth of passage 2 DPCs, and the inhibitory effect was significant 3 days after RNAi treatment. The mRNA and protein levels of versican were also downregulated in passage 2 DPCs, and were lower than levels in nonaggregative passage 8 DPCs. Notably, the aggregative growth of nonaggregative passage 8 DPCs was restored after induction in a 1 : 1 v/v mixture of fresh DMEM and medium recycled from a previous passage.

CONCLUSION

Versican is a key gene for the aggregative growth of DPCs, and might be significant in the regeneration of HF.

Engineering nanoassemblies of polysaccharides

Polysaccharides offer a wealth of biochemical and biomechanical functionality that can be used to develop new biomaterials. In mammalian tissues, polysaccharides often exhibit a hierarchy of structure, which includes assembly at the nanometer length scale. Furthermore, their biochemical function is determined by their nanoscale organization. These biological nanostructures provide the inspiration for developing techniques to tune the assembly of polysaccharides at the nanoscale. These new polysaccharide nanostructures are being used for the stabilization and delivery of drugs, proteins, and genes, the engineering of cells and tissues, and as new platforms on which to study biochemistry. In biological systems polysaccharide nanostructures are assembled via bottom-up processes. Many biologically derived polysaccharides behave as polyelectrolytes, and their polyelectrolyte nature can be used to tune their bottom-up assembly. New techniques designed to tune the structure and composition of polysaccharides at the nanoscale are enabling researchers to study in detail the emergent biological properties that arise from the nanoassembly of these important biological macromolecules.

ADAMTS proteases: key roles in atherosclerosis?

The ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) proteases are secreted enzymes that regulate extracellular matrix turnover by degrading specific matrix components. Roles for the proteases in inflammation and atherosclerosis have been suggested by a number of recent studies, and the role of ADAMTS-4 and -5 in the breakdown of aggrecan and subsequent degradation of cartilage during osteoarthritis has also been established. The ability of the ADAMTS proteases to degrade versican, the primary proteoglycan in the vasculature, is thought to be central to any hypothesized role for the proteases in atherosclerosis. In this review, we introduce the structure and function of the ADAMTS family of proteases and review the literature that links them with inflammation and atherosclerosis.

Extracellular matrix molecules: potential targets in pharmacotherapy

The extracellular matrix (ECM) consists of numerous macromolecules classified traditionally into collagens, elastin, and microfibrillar proteins, proteoglycans including hyaluronan, and noncollagenous glycoproteins. In addition to being necessary structural components, ECM molecules exhibit important functional roles in the control of key cellular events such as adhesion, migration, proliferation, differentiation, and survival. Any structural inherited or acquired defect and/or metabolic disturbance in the ECM may cause cellular and tissue alterations that can lead to the development or progression of disease. Consequently, ECM molecules are important targets for pharmacotherapy. Specific agents that prevent the excess accumulation of ECM molecules in the vascular system, liver, kidney, skin, and lung; alternatively, agents that inhibit the degradation of the ECM in degenerative diseases such as osteoarthritis would be clinically beneficial. Unfortunately, until recently, the ECM in drug discovery has been largely ignored. However, several of today's drugs that act on various primary targets affect the ECM as a byproduct of the drugs' actions, and this activity may in part be beneficial to the drugs' disease-modifying properties. In the future, agents and compounds targeting directly the ECM will significantly advance the treatment of various human diseases, even those for which efficient therapies are not yet available.

The intracranial aneurysm susceptibility genes HSPG2 and CSPG2 are not associated with abdominal aortic aneurysm

BACKGROUND

A genetic variant on chromosome 9p21 associates with abdominal aortic aneurysm (AAA) and intracranial aneurysm (IA), indicating that despite the differences in pathology there are shared genetic risk factors. We investigated whether the IA susceptibility genes heparan sulfate proteoglycan 2 (HSPG2) and chondroitin sulfate proteoglycan 2 (CSPG2) associate with AAA as well.

METHODS

Using tag single nucleotide polymorphisms (SNPs), all common variants were analyzed in a Dutch AAA case-control population in a 2-stage genotyping approach. In stage 1, 12 tag SNPs in HSPG2 and 22 tag SNPs in CSPG2 were genotyped in 376 patients and 648 controls. Genotyping of significantly associated SNPs was replicated in a second independent cohort of 360 cases and 376 controls.

RESULTS

In stage 1, no HSPG2 SNPs and 1 CSPG2 SNP associated with AAA (rs2652106, P = .019). Association of this SNP was not replicated (P = .342).

CONCLUSIONS

Our findings demonstrate that, in contrast to IA, HSPG2 and CSPG2 do not associate with AAA.

Synthesis and organization of hyaluronan and versican by embryonic stem cells undergoing embryoid body differentiation

Embryonic stem cells (ESCs) provide a convenient model to probe the molecular and cellular dynamics of developmental cell morphogenesis. ESC differentiation in vitro via embryoid bodies (EBs) recapitulates many aspects of early stages of development, including the epithelial-mesenchymal transition (EMT) of pluripotent cells into more differentiated progeny. Hyaluronan and versican are important extracellular mediators of EMT processes, yet the temporal expression and spatial distribution of these extracellular matrix (ECM) molecules during EB differentiation remains undefined. Thus, the objective of this study was to evaluate the synthesis and organization of hyaluronan and versican by using murine ESCs during EB differentiation. Hyaluronan and versican (V0 and V1 isoforms), visualized by immunohistochemistry and evaluated biochemically, accumulated within EBs during the course of differentiation. Interestingly, increasing amounts of a 70-kDa proteolytic fragment of versican were also detected over time, along with ADAMTS-1 and -5 protein expression. ESCs expressed each of the hyaluronan synthases (HAS) -1, -2, and -3 and versican splice variants (V0, V1, V2, and V3) throughout EB differentiation, but HAS-2, V0, and V1 were expressed at significantly increased levels at each time point examined. Hyaluronan and versican exhibited overlapping expression patterns within EBs in regions of low cell density, and versican expression was excluded from clusters of epithelial (cytokeratin-positive) cells but was enriched within the vicinity of mesenchymal (N-cadherin-positive) cells. These results indicate that hyaluronan and versican synthesized by ESCs within EB microenvironments are associated with EMT processes and furthermore suggest that endogenously produced ECM molecules play a role in ESC differentiation. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Polyinosine-polycytidylic acid stimulates versican accumulation in the extracellular matrix promoting monocyte adhesion

Viral infections are known to exacerbate asthma and other lung diseases in which chronic inflammatory processes are implicated, but the mechanism is not well understood. The viral mimetic, polyinosine-polycytidylic acid, causes accumulation of a versican- and hyaluronan-enriched extracellular matrix (ECM) by human lung fibroblasts with increased capacity for monocyte adhesion. The fivefold increase in versican retention in this ECM is due to altered compartmentalization, with decreased degradation of cell layer-associated versican, rather than an increase in total accumulation in the culture. This is consistent with decreased mRNA levels for all of the versican splice variants. Reduced versican degradation is further supported by low levels of the epitope, DPEAAE, a product of versican digestion by a disintegrin-like and metallopeptidase with thrombospondin type 1 motif enzymes, in the ECM. The distribution of hyaluronan is similarly altered with a 3.5-fold increase in the cell layer. Pulse-chase studies of radiolabeled hyaluronan show a 50% reduction in the rate of loss from the cell layer over 24 hours. Formation of monocyte-retaining, hyaluronidase-sensitive ECMs can be blocked by the presence of anti-versican antibodies. In comparison, human lung fibroblasts treated with the cytokines, IL-1beta plus TNF-alpha, synthesize increased amounts of hyaluronan, but do not retain it or versican in the ECM, which, in turn, does not retain monocytes. These results highlight an important role for versican in the hyaluronan-dependent binding of monocytes to the ECM of lung fibroblasts stimulated with polyinosine-polycytidylic acid.

The biological role and regulation of versican levels in cancer

Increased expression of the proteoglycan, versican is strongly associated with poor outcome for many different cancers. Depending on the cancer type, versican is expressed by either the cancer cells themselves or by stromal cells surrounding the tumor. Versican plays diverse roles in cell adhesion, proliferation, migration and angiogenesis, all features of invasion and metastasis. These wide ranging functions have been attributed to the central glycosaminoglycan-binding region of versican, and to the N-(G1) and C-(G3) terminal globular domains which collectively interact with a large number of extracellular matrix and cell surface structural components. Here we review the recently identified mechanisms responsible for the regulation of versican expression and the biological roles that versican plays in cancer invasion and metastasis. The regulation of versican expression may represent one mechanism whereby cancer cells alter their surrounding microenvironment to facilitate the malignant growth and invasion of several tumor types. A greater understanding of the regulation of versican expression may contribute to the development of therapeutic methods to inhibit versican function and tumor invasion.

Cell death-associated ADAMTS4 and versican degradation in vascular tissue

High blood flow through baboon polytetrafluorethylene aorto-iliac grafts increases neointimal vascular smooth muscle cell (SMC) death, neointimal atrophy, and cleavage of versican to generate the DPEAAE neoepitope, a marker of ADAMTS-mediated proteolysis. In this study, we have determined the effect of high blood flow on transcript abundance in the neointima for ADAMTS1, -4, -5, -8, -9, -15, and -20. We found that after 24 hr of flow, the mRNA for ADAMTS4 was significantly increased, whereas that for the other family members was unchanged. Because vascular SMC death is markedly increased in the graft after 24 hr of high flow, we next examined the possibility that the ADAMTS4 induction and the cell death are causally related. The addition of Fas ligand to SMC cultures increased both ADAMTS4 mRNA and cell death approximately 5-fold, consistent with the idea that ADAMTS4-dependent cleavage of versican may be partly responsible for cell death and tissue atrophy under these conditions.

ADAMTS-7 Mediates Vascular Smooth Muscle Cell Migration and Neointima Formation in Balloon-Injured Rat Arteries

The migration of vascular smooth muscle cells (VSMCs) plays an essential role during the development of atherosclerosis and restenosis. Extensive studies have implicated the importance of extracellular matrix (ECM)-degrading proteinases in VSMC migration. A recently described family of proteinases, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTs), is capable of degrading vascular ECM proteins. Here, we sought to determine whether ADAMTS-7 is involved in VSMC migration and neointima formation in response to vascular injury. ADAMTS-7 protein accumulated preferentially in neointima of the carotid artery wall after balloon injury. In primary VSMCs, ADAMTS-7 level was enhanced by the proinflammatory cytokine tumor necrosis factor α and growth factor platelet-derived growth factor-BB. ADAMTS-7 overexpression greatly accelerated and small interfering RNA knockdown markedly retarded VSMC migration/invasion in vitro. In addition, luminal delivery of ADAMTS-7 adenovirus to carotid arteries exacerbated intimal thickening nearly sixfold 7 days after injury. Conversely, perivascular administration of ADAMTS-7 small interfering RNA but not scramble small interfering RNA to injured arteries attenuated intimal thickening by 50% at 14 days after injury. Furthermore, ADAMTS-7 mediated degradation of the vascular ECM cartilage oligomeric matrix protein (COMP) in injured vessels. Replenishing COMP circumvented the promigratory effect of ADAMTS-7 on VSMCs. Enforced expression of COMP significantly suppressed VSMC migration and neointima formation postinjury, which indicates that ADAMTS-7 facilitated intimal hyperplasia through degradation of inhibitory matrix protein COMP. ADAMTS-7 may therefore serve as a novel therapeutic target for atherosclerosis and postangioplasty restenosis.

A HaemAtlas: characterizing gene expression in differentiated human blood cells

Hematopoiesis is a carefully controlled process that is regulated by complex networks of transcription factors that are, in part, controlled by signals resulting from ligand binding to cell-surface receptors. To further understand hematopoiesis, we have compared gene expression profiles of human erythroblasts, megakaryocytes, B cells, cytotoxic and helper T cells, natural killer cells, granulocytes, and monocytes using whole genome microarrays. A bioinformatics analysis of these data was performed focusing on transcription factors, immunoglobulin superfamily members, and lineage-specific transcripts. We observed that the numbers of lineage-specific genes varies by 2 orders of magnitude, ranging from 5 for cytotoxic T cells to 878 for granulocytes. In addition, we have identified novel coexpression patterns for key transcription factors involved in hematopoiesis (eg, GATA3-GFI1 and GATA2-KLF1). This study represents the most comprehensive analysis of gene expression in hematopoietic cells to date and has identified genes that play key roles in lineage commitment and cell function. The data, which are freely accessible, will be invaluable for future studies on hematopoiesis and the role of specific genes and will also aid the understanding of the recent genome-wide association studies.

Characterization of proADAMTS5 processing by proprotein convertases

ADAMTS5 (aggrecanase-2), a key metalloprotease mediating cartilage destruction in arthritis, is synthesized as a zymogen, proADAMTS5. We report a detailed characterization of the propeptide excision mechanism and demonstrate that it is a major regulatory step with unusual characteristics. Using furin-deficient cells and a furin inhibitor, we found that proADAMTS5 was processed by proprotein convertases, specifically furin and PC7, but not PC6B. Mutagenesis of three sites containing basic residues within the ADAMTS5 propeptide (RRR(46), RRR(69) and RRRRR(261)) suggested that proADAMTS5 processing occurs after Arg(261). That furin processing was essential for ADAMTS5 activity was illustrated using the known ADAMTS5 substrate aggrecan, as well as a new substrate, versican, an important regulatory proteoglycan during mammalian development. When compared to other ADAMTS proteases, proADAMTS5 processing has several distinct features. In contrast to ADAMTS1, whose furin processing products were clearly present intracellularly, cleaved ADAMTS5 propeptide and mature ADAMTS5 were found exclusively in the conditioned medium. Despite attempts to enhance detection of intracellular proADAMTS5 processing, such as by immunoprecipitation of total ADAMTS5, overexpression of furin, and secretion blockade by monensin, neither processed ADAMTS5 propeptide nor the mature enzyme were found intracellularly, which was strongly suggestive of extracellular processing. Extracellular ADAMTS5 processing was further supported by activation of proADAMTS5 added exogenously to HEK293 cells stably expressing furin. Unlike proADAMTS9, which is processed by furin at the cell-surface, to which it is bound, ADAMTS5 does not bind the cell-surface. Thus, the propeptide processing mechanism of ADAMTS5 has several points of distinction from those of other ADAMTS proteases, which may have considerable significance in the context of osteoarthritis.

Athsq1 is an atherosclerosis modifier locus with dramatic effects on lesion area and prominent accumulation of versican

OBJECTIVE

Susceptibility to atherosclerosis is genetically complex, and modifier genes that do not operate via traditional risk factors are largely unknown. A mouse genetics approach can simplify the genetic analysis and provide tools for mechanistic studies.

METHODS AND RESULTS

We previously identified atherosclerosis susceptibility QTL (Athsq1) on chromosome 4 acting independently of systemic risk factors. We now report confirmation of this locus in congenic strains carrying the MOLF-derived susceptibility allele in the C57BL/6J-Ldlr(-/-) genetic background. Homozygous congenic mice exhibited up to 4.5-fold greater lesion area compared to noncongenic littermates (P<0.0001). Analysis of extracellular matrix composition revealed prominent accumulation of versican, a presumed proatherogenic matrix component abundant in human lesions but almost absent in the widely-used C57BL/6 murine atherosclerosis model. The results of a bone marrow transplantation experiment suggested that both accelerated lesion development and versican accumulation are mediated, at least in part, by macrophages. Interestingly, comparative mapping revealed that the Athsq1 congenic interval contains the mouse region homologous to a widely-replicated CHD locus on human chromosome 9p21.

CONCLUSIONS

These studies confirm the proatherogenic activity of a novel gene(s) in the MOLF-derived Athsq1 locus and provide in vivo evidence for a causative role of versican in lesion development.

ADAMTS-4 and -8 are inflammatory regulated enzymes expressed in macrophage-rich areas of human atherosclerotic plaques

OBJECTIVES

Remodeling of extracellular matrix (ECM) plays an important role in inflammatory disorders such as atherosclerosis. ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) is a recently described family of proteinases that is able to degrade the ECM proteins aggrecan and versican expressed in blood vessels. The purpose of the present study was to analyze the expression and regulation of several ADAMTSs before and after macrophage differentiation and after stimulation with IFN-gamma, IL-1beta and TNF-alpha. ADAMTS expression was also examined during atherosclerosis development in mice and in human atherosclerotic plaques.

METHODS AND RESULTS

Real time RTPCR showed that, of the nine different ADAMTS members examined, only ADAMTS-4 and -8 were induced during monocyte to macrophage differentiation, which was also seen at protein level. Macrophage expression of ADAMTS-4, -7, -8 and -9 mRNA were enhanced upon stimulation with IFN-gamma or TNF-alpha. Furthermore, immunohistochemical analyses revealed that ADAMTS-4 and -8 were expressed in macrophage rich areas of human atherosclerotic carotid plaques and coronary unstable plaques. In addition, ADAMTS-4 expression was upregulated during the development of atherosclerosis in LDLR(-/-)ApoB(100/100) mice. Whereas ADAMTS-4 expression was low in non-atherosclerotic aortas, it was significantly higher in aortas from 30-40-week old atherosclerotic animals.

CONCLUSION

The present study suggests that ADAMTS-4 and -8 are inflammatory regulated enzymes expressed in macrophage-rich areas of atherosclerotic plaques. This is the first study associating ADAMTS-4 and -8 expression with atherosclerosis. However, further experiments are required to understand the physiological and pathological functions of ADAMTS in the vascular wall, and tools to measure ADAMTS activity need to be developed.

Extracellular matrix in the trabecular meshwork

The extracellular matrix (ECM) of the trabecular meshwork (TM) is thought to be important in regulating intraocular pressure (IOP) in both normal and glaucomatous eyes. IOP is regulated primarily by a fluid resistance to aqueous humor outflow. However, neither the exact site nor the identity of the normal resistance to aqueous humor outflow has been established. Whether the site and nature of the increased outflow resistance, which is associated with open-angle glaucoma, is the same or different from the normal resistance is also unclear. The ECMs of the TM beams, juxtacanalicular region (JCT) and Schlemm's canal (SC) inner wall are comprised of fibrillar and non-fibrillar collagens, elastin-containing microfibrils, matricellular and structural organizing proteins, glycosaminoglycans (GAGs) and proteoglycans. Both basement membranes and stromal ECM are present in the TM beams and JCT region. Cell adhesion proteins, cell surface ECM receptors and associated binding proteins are also present in the beams, JCT and SC inner wall region. The outflow pathway ECM is relatively dynamic, undergoing constant turnover and remodeling. Regulated changes in enzymes responsible for ECM degradation and biosynthetic replacement are observed. IOP homeostasis, triggered by pressure changes or mechanical stretching of the TM, appears to involve ECM turnover. Several cytokines, growth factors and drugs, which affect the outflow resistance, change ECM component expression, mRNA alternative splicing, cellular cytoskeletal organization or all of these. Changes in ECM associated with open-angle glaucoma have been identified.